1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling the angle of trim of the propulsion unit of a ship such as a motorboat.
2. Description of the Relevant Art
FIGS. 5A and 5B show a small ship 100 such as a motorboat having a hull 101 and a propulsion unit 102 such as an outboard motor mounted on the stern of the hull 101. The propulsion unit 102 is angularly adjustable with respect to the hull 101 so that the angle .theta. of tilt of the propulsion unit 102 with respect to the horizontal central axis of the hull 101 is variable for producing propulsive forces efficiently. More specifically, a pair of laterally spaced transom brackets 103 is attached to the stern of the hull 101 such that the transom brackets 103 are symmetrically positioned with respect to a vertical plane which contains the longitudinal central axis of the hull 101. Between the transom brackets 103, there is pivotally coupled a swivel bracket (not shown) which is vertically and horizontally angularly movable, with the propulsion unit 102 mounted on the swivel bracket. The angle .theta. of tilt of the propulsion unit 101 is detected by a tilt angle sensor (not shown) disposed between the propulsion unit 102 and one of the transom brackets 103. A leveling sensor (not shown) for detecting the angle .beta. at which the propulsion unit 102 is slanted with respect to the horizontal plane is mounted on the propulsion unit 102 itself. The angle .theta. of tilt of the propulsion unit 102, the angle .beta. of the propulsion unit 102 from the horizontal plane, and the angle of trim can be varied by a tilt and trim unit 104 disposed between the transom brackets 103.
More specifically, the tilt and trim unit 104 is actuated by a control circuit (not shown) based on signals from the leveling sensor and the tilt angle sensor so that the propulsion unit 102 produces horizontal propulsive thrust at all times either when the motorboat 100 is at rest or planes as shown in FIG. 5A or immediately after the motorboat 100 is accelerated as shown in FIG. 5B.
Fuel consumption by the propulsion unit 102 is better while the motorboat 100 is planing. Right after the motorboat 100 is accelerated, the stem of the hull 101 is lifted off the water as shown in FIG. 5B. If the angle of trim is varied to produce horizontal propulsive thrust as described above when the stem is lifted as shown in FIG. 5B, then the stem is further lifted upwardly. As a result, the motorboat 100 cannot plane, does not give the boatsman a sufficiently wide front view for maneuvering, and suffers bad fuel economy.
The present invention has been made in an effort to effectively solve the above problems of the conventional method of controlling the angle of trim of a marine propulsion unit.